Use the free VUplug for audio metering from our colleagues at musicIO
In case you didn't know already, musicIO is the best solution for MIDI and Audio using a regular Lightning-USB cable.
musicIO :: audio and MIDI over USB
How Can I Get a Meter Control in MIDI Designer?
- Create a Slider
- Change the Display Option to Meter

- Also works for Crossfaders! (change type in actions)